In order to reexamine the Pediastrum boryannum complex in Korea, 10 strains of Pediastrum boryanum complex were isolated from 10 different locations in Korea and were cultured in the laboratory. Ultrastructure of the cell wall, the cell shape, and the processes on the peripheral cells were examined. The isolates were classified as P.boryanum var. boryanum, P. boryanum var. brevicorne which is reported for the first time in Korea, and P. boryanum var. longicorne. The previously reported taxa, P. boryanum var. brevicorne f. punctulatum was included in P. boryanum var. brevicorne. P. boryanum var.rugulosum was classified as P. angulosum. The cell wall ultrastructure and the length of the processes on the peripheral cells were the most distinctive characters for infraspecific classification of P. boryanum.